Biology subjects

Lessard, J.-P.

Publications and source records attributed to Lessard, J.-P..

3 recordsLinked to original sources

bioRxiv2025

The macroecology of immunity: predominant influence of climate on invertebrate immune response

The immune system is the primary defense against parasites. With the ever-increasing rate of disease, epidemiologic models considering geographic variation in immune responses could prove useful. Despite increasing interest in the macroecology of parasitism and infectious diseases, we know little about the macroecology of immune responses. Host characteristics, parasite exposure, and environmental factors can all affect immunity, but how these factors interact to shape spatial variation in the strength of immune responses remains unexplored. We captured odonates (dragonflies and damselflies) and their conspicuous ectoparasitic mites across a geographic area spanning the temperate and boreal forest biomes in eastern Canada. We then conducted immune response bioassays on 1,237 individuals from 63 odonate species. We used linear regressions and structural equation models to relate immune responses to host body size, parasite load, pH, temperature, and precipitation while accounting for evolutionary relationships among host species. We found significant differences in the strength of immune response among host individuals, and this variation was best explained by climatic conditions, specifically decreasing with precipitation and, to a lesser degree, temperature. While host species significantly differed in immune response strength, we found no effect of host body size, evolutionary relationships among hosts, or parasitism on immune response. Our study investigating the drivers of immune response across dozens of species spread across two biomes is the most comprehensive to date. Climatic conditions have a strong influence on host immune response, regardless of host characteristics or parasitism rates. In this specific case, strong immune responses were associated with low levels of annual precipitation, which could relate to the role of cuticular melanin content in desiccation resistance, and the melanin-based encapsulation response being a byproduct of this adaptation. A spatially-explicit understanding of the biological processes affecting immunity could improve epidemiological models of disease risk that inform disease management globally.

immunology↗

bioRxiv2024

Thrifty superorganism phenotypes emerge as a plastic response to extreme environments in the Hercules ant

AO_SCPLOWBSTRACTC_SCPLOWAdaptation to extreme environments is commonly assumed to occur through microevolutionary change. However, studies of high-altitude human populations show that organisms can also respond to nutritional stress through developmental plasticity, producing thrifty phenotypes that prioritize essential function over costly structures. Whether this adaptive strategy extends beyond humans, and how it operates in natural systems, remains largely unexplored. Here, we test the thrifty phenotype hypothesis (TPH) in a widely distributed superorganism, the carpenter ant Camponotus herculeanus, which inhabits some of the most environmentally challenging regions of the Northern Hemisphere. Colonies comprise inexpensive minor workers and energetically costly major workers, providing a powerful system for examining plastic investment under resource limitation. We quantified relationships between caste structure and climate and conducted a common-garden experiment to test the TPH. We show that the proportion of major workers declines with increasing latitude, independently of body size and colony size, and is best predicted by the number of days, annually, during which workers can nurse brood. Experimental results further demonstrate that colonies rapidly and plastically adjust caste structure in response to environmental conditions. Our findings reveal that thrifty phenotypes can emerge in superorganisms and could represent a conserved developmental response to environmental stress. By extending a central hypothesis from human biology to social insects, this work provides a unifying framework for understanding how developmental plasticity shapes adaptation across levels of biological organization.

ecology↗

bioRxiv2022

Population demography maintains biogeographic boundaries

Global biodiversity is organized into biogeographic regions that comprise distinct biotas. The contemporary factors maintaining differences in species composition between biogeographic regions are poorly understood. Given the evidence that populations with sufficient genetic variation can adapt to fill new habitats, it is surprising that we do not see more homogenization of species assemblages among regions. Theory suggests that the expansion of populations across biogeographic transition zones could be limited by environmental gradients that affect population demography in ways that could limit adaptive capacity, but this has not been empirically explored. Using three independently curated data sets describing continental patterns of mammalian demography and population genetics, we show that populations closer to biogeographic transition zones have lower effective population sizes and genetic diversity, and are more genetically differentiated. These patterns are consistent with reduced adaptive capacity near biogeographic transition zones. The consistency of these patterns across mammalian species suggests they are stable, predictable, and generalizable in their contribution to long-term limits on expansion and homogenization of biodiversity across biogeographic transition zones. Understanding the contemporary processes acting on populations that maintain differences in the composition of regional biotas is crucial for our basic understanding of the current and future organization of global biodiversity. The importance of contemporary, population-level processes on the maintenance of global biogeographic regions suggests that biogeographic boundaries are susceptible to environmental perturbation associated with human-caused global change.

ecology↗